Airport engineering-c

Airport Engineering

Fall Semester

Sept 11 to Jan 12He who knows and knows he knows: he is wise ‐

Lecture – 4

CE – 241follow him. Chinese Proverb Transportation Engineering‐1(NIT‐SCEE‐

NUST)

Runway Length EstimationRunway Length EstimationAccording to FAA AC 150/5325-4

Transportation Engineering‐1(NIT‐SCEE‐NUST)

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Runway

Length can be obtained from: -a. Approximate runway lengths are 12000’ for large airplanes pp y g g pb. Flight manual (corrected for wind and gradient as well)c. Publications by aircraft manufacturers containing runway lengthdiagrams for runway planning and design.d. Performance curves by FAA are utilized. Two types of procedures :

one is based upon aircraft performance curves and other on aircraft p pperformance charts. Data required includes:-

(1) Critical aircraft?(2) Longest non stop ro te distance?(2) Longest non-stop route distance?(3) T/O and Landing weights?(4) Airport elevation?( ) p(5) Mean daily maximum temperatures for the hottest month?(6) Max elevation difference of runway centreline. 3

Declared Distances (ICAO speci)Declared Distances (ICAO speci)

(a) Take-off Run Available (TORA): The length of runway declared available and suitable for the ground run of an aeroplane taking off.

(b) Takeoff Distance Available (TODA): The length of the takeoff run ( ) ( ) gavailable plus the length of the clearway, where provided. (Maximum clearway length allowed is 1 000 ft. and the clearway length allowed must lie within the aerodrome or airport boundary).

(c) Accelerate Stop Distance Available (ASDA): The length of the takeoff run available plus the length of the stopway, where provided. p g p y, p

(d) Landing Distance Available (LDA): The length of runway which is declared available and suitable for the ground run of an aeroplane landingdeclared available and suitable for the ground run of an aeroplane landing.


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Displaced Threshold


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Sequence

– Computation of Runway Length• Performance requirements of aircrafts for runway length.

• Environs on the airportEnvirons on the airport.

6Transportation Engineering‐1(NIT‐SCEE‐

NUST)

Computation of Runway LengthComputation of Runway Length

Basic Conditions assumed:• No wind is blown on runway• Aircraft is loaded with full loading capacity• Airport is at sea level• No wind is blowing on the way to destination• Runway is levelled i.e. Zero positive gradient• Standard temperature of 15 0C at the airport• Standard temperature exists along the way• Standard temperature exists along the way


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Computation of Runway LengthComputation of Runway Length

Factors effecting runway length:g y g

Performance Requirements of Aircrafts i.e. power & Propulsion system, Type of aircraft , etc

E i t th Ai tEnvirons at the Airport

Safety Requirement i e Takeoff condition Landing conditionSafety Requirement i.e. Takeoff condition ,Landing condition & emergency condition.


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HeliportsHeliports

Because of the unique operational characteristics of helicopters, heliportphysical characteristics are significantly different from the physicalphysical characteristics are significantly different from the physicalcharacteristics of aerodromes. For instance, there is no requirement for arunway at a heliport. In addition, the heliport FATO size is 1.5 times largerthan the longest helicopter for which the heliport is certified. A safety areasurrounds the FATO, which is to be kept free of obstacles other than visualaids.


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Environs at the airportEnvirons at the airport

• Temperature. Higher the temperature, the longer the runway p g p , g yrequired because of lower air densities resulting in lower out-put of thrust. Relationship is non linear.

• Surface Wind. Greater the headwind, shorter will be the runway. No wind is considered for airport planning purposes.

• Runway Gradient. An uphill gradient requires more runway length than a level or downhill gradient, the specific amount depending on g , p p gthe elevation airport and the temperature. Relationship is nearly linear. For turbine powered aircrafts it amounts to 7 to 10 % for each 1 % of uniform gradient (max 1.5 %).e c % o u o g d e ( .5 %).


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Temperature effectTemperature effect

• Reduces air density if aircraft is located within stratosphere (up to y p ( p11km height above sea level) and temperature decreases

• Reduce density reduce drag force while landing or require longer• Reduce density reduce drag force while landing or require longer distance for producing necessary lift for aircraft to fly.

• Increase basic runway length, 1 % for every I C rise in airport reference temperature above the standard temperature at that elevation.


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Environs at the airportEnvirons at the airport

• Altitude. All other things being equal, the higher the altitude of the g g q , gairport, the longer the runway required. This increase is not linear but varies with weight and temperature. For planning purposes an increase from sea level of 7 percent per 1000 ft (300m) of altitude p p ( )will suffice for most airport sites except those that experience very hot temperatures or are located at high altitudes. Then the rate of increase can be as much as 10 percent.increase can be as much as 10 percent.

• Condition of Runway Surface. Slush, wet snow or standing water makes braking extremely poor and causes a significant retarding force especially on takeoff to the extent that takeoff may not takesforce, especially on takeoff to the extent that takeoff may not takes place. Jet operations are limited to no more than 0.5 in of slush or water. Between 0.25 and 0.5 in, the takeoff weight must be reduced. Ad t d i i dAdequate drainage required.


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General Federal Aviation RegulationCriteria to Develop Runway LengthCriteria to Develop Runway Length

Requirements at Airports


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General Procedure for Runway LengthE i iEstimationRunways components:

• Full strength pavement (FS)• Clearways (CL)• Stopways (SW)

Full strength pavement should support the full weight of the aircraft

Cl i d b d S l f b l (Clearway is a prepared area are beyond FS clear of obstacles (max slope is 1.5%) allowing the aircraft to climb safely to clear an imaginary 11 m (35’ obstacle)

Stopway is a paved surface that allows and aircraft overrun to take place without harming the vehicle structurally (cannot be used for takeoff))


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FAR Certification ProceduresFAR Certification ProceduresFAR 25 (for turbojet and turbofan powered aircraft) consider three cases in the estimation of runway length performance:

• Normal takeoff (all engines working fine)E i t t k ff diti• Engine-out takeoff condition

- Continued takeoff- Aborted takeoff

• Landing

All these cases consider stochastic variations in piloting techniqueAll these cases consider stochastic variations in piloting technique (usually very large for landings and smaller for takeoffs)


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NomenclatureNomenclature

• FL = field length (total amount of runway needed)g ( y )• FS = full strength pavement distance• CL = clearway distance

S di• SW = stop way distance• LOD = lift off distance• TOR = takeoff runTOR takeoff run• TOD = takeoff distance• LD = landing distance• SD = stopping distance• D35 = distance to clear an 11 m (35 ft.) obstacle


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Landing Distance CaseLanding Distance Case

• The landing distance should be 67% longer than the demonstrated g gdistance to stop an aircraft Large landing roll variations exist among pilots assuming that the pilot makes an approach at the proper speed and crosses the threshold at a height of 50 ft. g


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Normal Landing ConditionNormal Landing Condition

StTouchdown point

15 mStop

Runway (Full strength)

60 % of Landing distance

RunwayThreshold

y ( g )

Landing distance

• 15m


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15m•60 % of landing distance

Normal Takeoff CaseNormal Takeoff Case

• The Takeoff Distance (TOD) should be 115% longer than the ( ) gdemonstrated Distance to Clearance 11m (35 ft.) obstacle (D35)


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Engine-Out Takeoff CaseEngine Out Takeoff Case

Dictated by two scenarios:

Continued takeoff case• A t l di t t l i i 11 (35 ft) b t l D35• Actual distance to clear an imaginary 11 m (35 ft) obstacle D35(with an engine-out)

Aborted or rejected takeoff case• Distance to accelerate and stop (DAS)


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Lift off pointEngine Failure

Accelerate to Vt

11m

Lift off point

Stop way

Decelerate Stop DistanceDecelerate Stop Distance

Lift of Distance Clearway > half this

Accelerate Stop Distance

Take off Distance


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To compute required field length expressions dused

• FL = max (TODn, TODeo, DAS, LD)FL max (TODn, TODeo, DAS, LD)• FS = max (TORn, TOReo, LD)• SW = DAS - max (TORn TOReo LD)SW DAS - max (TORn, TOReo, LD)• CL = min {(FL-DAS), CLn, CLeo}• SW min =0• SW min =0• CL min =0• CL 300 (1000 ft)• CL max = 300m (1000 ft)


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Problem‐1Problem 1• Determine the runway length requirements according to

specifications of FAR parts 25 and 121 for turbine‐poweredaircraft with following performance characteristics

All distances in feet

Normal landing, Stop distance 5000

Normal takeoff,Lift off distance 7000Lift‐off distanceDistance to 35‐ft height

70008000

Engine failure takeoffLift‐off distance 8200Lift off distanceDistance to 35‐ft height

82009100

Engine-failure, aborted takeoffAccelerate - Stop distance 9500


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p

Relationship of failure speed (Vf )with l h l drunway length, clearway and stopway

• For piston engine aircraft, full strength pavement provided for entire take off and accelerate stop distance (distance required to stop from the pointoff and accelerate stop distance (distance required to stop from the point where Vf was reached was equal to the distance from the same point to reach specified height of 11 m above the runway.) results in shortest runway or balanced runway length.

• For Turbine engine aircraft, not always results in shortest runway as

– CASE I: V=Vf , SW =CL =FL –FS , FS could be shortened a distance l t l b t t ld h t b t t d (b l dequal to clearway but a stopway would have to be constructed. (balanced

field length)

– CASE II: V<Vf , SW = 0, CL =FL –FS (Take off Distance or Distance to , , (D35) , Runway has been shortened but only clearway required.

– CASE III: V>Vf , SW= FL-FS , Runway length is minimum but DAS is greatly increasedgreatly increased


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Correction to basic runway lengthCorrection to basic runway length

Elevation correction rateElevation correction rate• Lc =7% per 300m rise above MSL (Le=Lc= 0.07 E +1)

Temperature correction rate• Lc =1% for every 1 degree rise in ART above Std Atm Tem at

that elevation (Lt in MKS =Lc =0.01{T‐(15‐1.981 E)} + 1)

G di iGradient Correction rate• Lc = 20% for every 1% of effective gradient (Lg =Lc =0.10 G

+ 1 where G = RL max‐RL min/L)+ 1 where G = RL max‐RL min/L)


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Problem 2• Publication of an aircraft manufacturer indicated the basic

Problem‐2

length of a runway for as particular aircraft as 4000 ft.Determine the length of runway if the altitude of the airportsite is 2500 ft effective gradient is 0 5% and mean ofsite is 2500 ft, effective gradient is 0.5% and mean ofmaximum daily temperatures for the hottest month is 360 Caveraged over 10 years.

a. Altitude correction

b. Temperature correction

G di ic. Gradient correction


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